Molded camshaft assembly

ABSTRACT

A camshaft assembly for an internal combustion engine includes a rotatable camshaft and a cam lobe mounted on the camshaft for rotation therewith. The cam lobe includes first and second axial ends and an integral crowned cam profile formed in its periphery which includes a radially extending shoulder located between the first and second ends. The shoulder may be formed by a pair of axially extending parallel tapered surfaces in the cam profile. A method of molding the camshaft assembly includes the steps of providing a mold including a die component closable to define a mold cavity having a first portion in the shape of a camshaft and a second portion in the shape of cam lobe which includes a crowned cam profile, filling the mold cavity with a shrinkable fluid plastics material, waiting a predetermined period of time to permit the plastics material in the second portion of the mold cavity to harden and shrink, and moving the die component in an axial direction to open the mold.

This is a continuation of application Ser. No. 07/168,142, filed Mar.14, 1988, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to camshaft assemblies, and moreparticularly to a molded camshaft assembly for an internal combustionengine.

Small internal combustion engines, such as those used on lawn mowers andsnow blowers, generally include a cam gear and at least one cam lobemounted on a camshaft. The camshaft is rotated by means of the cam gear,which, as is conventional, meshes with a timing gear on a crankshaft torotate in timed relation to the engine cycle. The cam lobe is used tocontrol an exhaust and an intake valve, as is also conventional.

In the past, such cam lobes have been formed of metallic materialsutilizing time consuming and expensive precision machining methods. Forexample, metallic cam lobes are generally made by utilizing a hobbingmachine to cut the cam lobe from a solid piece of metal. Hobbing camlobes may also result in undesirable high waste or scrap material whichfurther increases their cost of manufacture.

More recently, it has been found that non-metallic cam lobes may bemolded from plastics material with sufficient accuracy for smallinternal combustion engines. Such molded non-metallic cam lobes providefor reduced noise and lower cost compared with metallic cam lobes.

When the camshaft rotates in timed relation to the engine cycle, the camlobe rotates therewith and acts through cam followers that arepositioned to ride on the peripheral surface or profile of the cam lobeand are operatively connected with valves that are cyclically openedwhen the engine is running to control the intake and exhaust systems ofan internal combustion engine. If the follower rides on the edge of thecam lobe, excessive stress and pitting of the peripheral surface of thecam profile may occur. Crowning of the cam profile generally helps tosolve this problem. Crowning provides a profile such that the highestpoint of the cam lobe's peripheral surface which contacts the camfollower is at or near the center of the lobe. In order to crown the camprofile utilizing a conventional molding process, the die toolingtypically becomes more expensive and complex with the result that onlytwo cavities may be utilized with such mold compared with four cavitieswith simpler tooling. More specifically, if the cam mold tooling may bepulled off axially, the tooling is less expensive and complex and fourcavities may used in the mold. Normally, however, if axially movabletooling would be utilized to mold a cam lobe, the cam profile cannot becrowned since crowning would normally require the mold tooling to bepulled off radially at 90° to the camshaft axis. As a result,conventional molding techniques would require that a cam lobe have anaxially tapered cam profile to allow the tooling to be pulled offaxially. Unfortunately, with an axially tapered cam profile the followerwould ride on the high edge of the cam profile causing excessive wearand pitting, as noted above.

It is therefore desirable to provide a cam lobe which may be molded ofnon-metallic materials using a relatively inexpensive molding processwhich would provide a cam profile that avoids or eliminates excessivewear.

SUMMARY OF THE INVENTION

A camshaft assembly for an internal combustion engine.

In one aspect, the invention comprises a method of molding a camshaftassembly which includes a camshaft and integral cam lobe for an internalcombustion engine. The steps include providing a mold including a diecomponent closable to define a mold cavity having a first portion in theshape of a camshaft which defines an axis of rotation and a secondportion in the shape of a cam lobe which includes a crowned cam profile,filling the mold cavity with a shrinkable fluid plastics material,waiting a predetermined period of time to permit the plastics materialin the second portion of the mold cavity to harden and shrink, andmoving the die component in an axial direction to open the mold. Thefluid plastics material has a shrinkage rate of at least about 0.000067inches per second, and preferably comprises a heated molten plasticsmaterial such as unreinforced or reinforced nylon. When utilizing aheated molten plastics material with suitable shrinkage characteristicssuch as nylon, the step of waiting includes cooling the molten materialfor a period of time between 0 and 30 seconds, preferably less than 5seconds. Also, the filling step preferably is accomplished via injectionmolding techniques.

In another aspect of the invention, the camshaft assembly includes acamshaft defining an axis of rotation, and a stepped cam lobe mounted onthe camshaft or rotation therewith having first and second axial ends.The stepped cam lobe has an integral cam profile formed in itsperipheral surface which includes a shoulder located between the firstand second ends of the cam lobe which has a radial dimension equal to orgreater than the radial dimension of the first and second ends.

The stepped cam profile includes first and second axially extendingtapered surfaces with the first tapered surface extending axially fromthe first end to the shoulder, and the second tapered surface extendingaxially from the shoulder to the second end of the cam lobe.Additionally, the first and second tapered surfaces of the cam profilegenerally extend parallel to one another. The stepped profile causes atappet follower to contact the cam profile away from the edge of the camso that the cam follower rides away from the cam surface edge to reducewear and to enable the cam lobe to be produced by a relativelyinexpensive molding technique.

In a modified form of the stepped profile, the step in the centralregion of the profile is molded with exterior and interior radii tosmooth the transition.

In yet another aspect of the invention, the camshaft assembly comprisesa metal camshaft together with an all-plastic cam assembly mounted onthe camshaft for rotation therewith. Such a camshaft assembly isreferred to herein as a "composite" assembly. The all-plastic camassembly includes a cam gear, an exhaust cam lobe and an intake camlobe, each of which is axially spaced apart from one another andintegrally interconnected by a hollow sleeve member which surrounds themetal camshaft. Additionally, in still another aspect of the invention,the entire camshaft assembly including both the cam assembly and thecamshaft is composed of a plastics material and formed integrally withthe journal bearing ends of the sleeve member. Thus, an all-plasticcamshaft assembly is provided wherein the intake cam lobe, the exhaustcam lobe, the cam gear and the camshaft are each composed of a plasticsmaterial and integrally formed together as a one-piece assembly.

Benefits of making the camshaft assembly in either the composite form orentirely of non-metallic or plastics material include:

1. Quiet operation, due to resilient, damped gear tooth and bearingnon-metallic material used.

2. Quiet operation, due to low inertia and light weight of non-metallicmaterial used.

3. Quiet operation, due to smooth surface finish achievable in moldingof non-metallic material.

4. Desirable smooth surface finish is achievable as molded; thusexpensive grinding is not needed on cam lobes and bearing journals aswould be required with metal camshaft assemblies.

5. The levels of geometric accuracy and precision normally required formetal cam gear teeth and camshaft assembly bearings are not required forcamshaft assemblies made of plastics or non-metallic materials, becausenoise is not as sensitive to accuracy and precision when non-metallicsare used. For example, small nicks or gouges on gear teeth or cam lobeswill heal during normal operation, and will not cause excessive noise.

6. Bearings need not be as accurate because resilient materials willfacilitate small deformations which will facilitate load sharing andelastohydrodynamic action, allowing the bearings to carry unusually highbearing loads without excessive wear.

7. Camshaft assemblies made of plastics or non-metalic materials areless sensitive to stresses because the relatively resilient materialwill deform slightly and spread the loads of mating gear teeth and valvetappets.

8. To minimize stress and to promote low vibration and noise, it isdesirable to utilize polynomial cam lobe profiles, and to crown thelobes. If the lobes are crowned, the cam followers run at or near to thelobe axial centers, and the force application points will not move backand forth on the lobes.

Though normally these geometric shapes are expensive to achieve whenusing metals since expensive grinding is normally required, these shapescan be molded into the camshaft assembly at no extra cost using plasticsor non-metallic materials.

Crowning the lobes also has a beneficial effect to compensate for"sinking", which causes undesirable depressions in the middle of thelobes, caused by shrinkage during cooling. The material in the center ofthe lobes cools last, resulting in depressions unless the lobes arecrowned.

9. To minimize gear tooth stress which promotes long life, it isdesirable that a full root radius be used. Though normally this wouldrequire expensive unusual tooling to be used with metallic materials, itcan be molded at no significant extra cost into a part made of plasticsor non-metallic material.

10. Conical, or tapered gear teeth are desirable to promote low noisedue to improved tooth load pick-up and improved lubrication. Thoughnormally with metallic gears this shape would be difficult to obtain, itcan be easily achieved with molded plastics or non-metallic cam gearassemblies.

11. Compression-release function desired for easy engine starting can beachieved with camshaft assemblies made of plastic at no extra cost bymolding small bumps into the intake or exhaust cam lobe profiles. Incontrast, this would normally require extra effort to grind these shapesinto the cam lobe profiles of a metallic camshaft assembly.

12. Significant noise and noise quality improvements can be achievedusing plastics or non-metallics in camshaft assemblies, because thecontacts with mating parts of gear teeth, journal bearings, thrustbearings and cam lobes are made with resilient, damped material.

13. Use of plastics or non-metallic materials promotes improved life ofmating parts of the engine because the plastics or non-metallic materialhas a low-friction, non-abrasive rubbing action if any contact is made.

14. Camshaft assemblies made of plastics or non-metallic materials canbe design-optimized for use on relatively low-speed engines (less than5,000 rpm and preferably less than about 4,000 rpm) used for lawn-mowingapplications. Metallic camshaft assemblies tend to be over designed andrelatively expensive for this application.

15. Camshaft assemblies made of plastics or non-metallic materials canbe design-optimized for use on relatively short (but adequate) lifeengines (1,000 to 3,000 hours) used for lawn-mowing applications.Metallic camshaft assemblies tend to be over designed and relativelyexpensive for this application.

16. Gear diameter is usually a highly critical dimension when metalgears are used, because of noise, stress, wear and life considerations.When plastics or non-metallics materials are used for the cam gear thesuccessful operation is not as sensitive to this dimension. Noise,stress, wear and life appear to still be adequate, in spite of high orlow back lash, or even gear tooth interference. In addition to diameter,the gears do not have to be as round as they have to be when metal gearsare used.

17. When plastics or non-metallic materials are used for gear teeth, andloading occurs, as in a power take-off or auxiliary drive application,the teeth can bend slightly, sharing the load, minimizing wear,extending life and minimizing noise.

18. Low-cost tooling can be used to take advantage of the inherentshrinkage of the polymer resins.

19. Camshaft assemblies made entirely of plastics or non-metallicmaterials and with adequate life and quality can be manufactured at muchlower cost than with metals.

The non-metallic materials that would be considered for the making ofengine camshaft assemblies might include various grades of thermoplasticresins such as: nylon (castable and/or injection moldable grades),phenolics, liquid crystal polymers, and poly-amide-imide. In addition,various polymer blends might be considered. Various fillers, powders,reinforcement fibers, and solid lubricants might also be considered.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the best mode presently contemplated of carryingout the invention.

In the drawings:

FIG. 1 is a side view in elevation of a composite camshaft assemblyincluding a stepped cam lobe in accordance with the present invention;

FIG. 2 is a fragmentary end view of the camshaft assembly of FIG. 1taken along the plane of the line 2--2 in FIG. 1;

FIG. 3 is a fragmentary enlarged side view in elevation of the steppedcam profile for the cam lobe of FIG. 1;

FIG. 4 is a fragmentary enlarged side view in elevation of a modifiedstepped cam profile for the cam lobe of FIG. 1;

FIG. 5 is a fragmentary enlarged cross sectional view showing the diecomponents of a mold in their closed position for making the camshaftassembly of the present invention which illustrates a third embodimentof a cam lobe having an arcuate cam profile;

FIG. 6 is a fragmentary cross sectional view of an all-plastic camshaftassembly;

FIG. 7 is a fragmentary cross sectional view similar to FIG. 6 of asecond embodiment of a composite camshaft assembly utilizing a tubularmetal support insert; and

FIG. 8 is a fragmentary cross sectional view similar to FIGS. 6 and 7 ofa third embodiment of a composite camshaft utilizing a solid metalsupport insert.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, FIG. 1 illustrates a camshaft assembly,generally designated by the numeral 1, constituting a preferredembodiment of the present invention. The camshaft assembly 1 shown inFIG. 1 is specifically adapted for use in a small internal combustionengine of the type generally utilized with lawn mowers and snow blowers.However, as is readily obvious to those skilled in the art, the camshaftassembly 1 of the present invention may be adapted for use with othertypes of internal combustion engines as well as other types ofapparatus.

Camshaft assembly 1 includes a cam gear 2, an intake cam lobe 3 and anexhaust cam lobe 4 mounted on a camshaft 5 of an internal combustionengine. The camshaft 5 is rotated about an axis of rotation 6 in timedrelation to the engine cycle by means of cam gear 1, as is conventional,which meshes with a timing gear (not shown) on the engine crankshaft.Camshaft 5 includes journals 16, 17 at opposite ends thereof forsupporting camshaft assembly 1 in bearings (not shown) in the enginehousing, as is conventional. Cam lobe 3 is used to control an intakevalve (not shown) while cam lobe 4 is used to control an exhaust valve(not shown), as is also conventional.

In the embodiment illustrated in FIG. 1, cam gear 2 and cam lobes 3 and4 are integrally molded together of a plastics material, such asreinforced or unreinforced nylon, as a one-piece assembly and areinterconnected by means of a hollow sleeve 7 to form an integralall-plastic cam assembly. Camshaft 5, in turn, consists of a unitarysolid member composed of a metallic material, and is of circular crosssection about which the integral cam assembly consisting of cam gear 2,cam lobes 3 and 4 and sleeve 7 are fixedly mounted. This camshaftassembly is referred to herein as a "composite" camshaft assembly.

Referring now to FIG. 7, there is illustrated a second embodiment of acomposite camshaft assembly. In this second embodiment, camshaft 5aconsists of a unitary tubular member composed of a metallic material,and is of circular cross section about which the integral cam assemblyconsisting of the cam gear, cam lobes (only intake cam lobe 3a beingshown) and sleeve 7a are fixedly mounted. Note that the ends of camshaft5a are covered by plastics material to form the journals (only journal16a being shown). Thus, camshaft 5a functions merely as a stiffening orsupport insert in this embodiment.

FIG. 8 illustrates a third embodiment of a composite camshaft assembly,and shows an intake cam lobe 3b, sleeve 7b and journal 16b of anintegral plastics cam assembly fixedly mounted on a camshaft 5b. Thisthird embodiment is thus similar to the second embodiment of FIG. 7except camshaft 5b is a unitary solid metallic member of circular crosssection. Additionally, and similar to the second embodiment, camshaft 5bfunctions merely as a stiffening or support insert.

It should be noted, however, that camshaft 5 may also be composed of aplastics material such as reinforced or unreinforced nylon, as well asother plastics materials, if desired. Under such circumstances, camshaft5 would not consist of a separate metallic member as shown in FIGS. 1, 7and 8 extending through sleeve 7 and the entire integral cam assembly.Instead, hollow sleeve 7 would essentially become the camshaft withjournals 16, 17 also comprising hollow members integrally attached toopposite ends of sleeve 7 to form an integral one-piece "all-plastic"camshaft assembly. This all-plastic camshaft assembly is illustrated inFIG. 6 showing an intake cam lobe 3c, sleeve 7c and journal 16c.

The non-metallic materials that would be considered for the making ofeither the composite or all-plastic engine camshaft assemblies mightinclude various grades of thermoplastic resins such as: nylon (castableand/or injection moldable grades), phenolics, liquid crystal polymers,and poly-amide-imide. In addition, various polymer blends might beconsidered. Various fillers, powders, reinforcement fibers, and solidlubricants might also be considered.

Castable nylon performs quite well, but the processing appears to berelatively expensive. Phenolic material cost is relatively low, butprocessing involves relatively high cost because of relatively long moldcycle times. The phenolic material can be molded very accurately, but itis very hard and brittle. To improve toughness, it preferably isreinforced with glass or other fiber, or fiberglass cloth. Thesereinforcing materials, however, may increase cost and/or cause abrasivewear of mating parts. Liquid crystal polymers (LCP'S) would perform wellin the engine. However, they are fairly new, and material cost appearsto be relatively high. Poly-amide-imide material (trade name "Torlon")appears to have excellent high temperature strength, but it appears tobe somewhat hard and brittle, and cost also appears to be relativelyhigh. Injection moldable nylon performs well, and costs of material andprocessing are relatively low. Stresses appear to be at or beyondrecommended limits at engine operating temperatures, but the cam lifestill appears to be adequate. Injection molded nylon appears to be thebest choice for small engines without "over-design", and high shrinkagein the mold makes possible the use of low-cost tooling.

As shown best in FIG. 2, cam lobes 3 and 4 include profiles 8 and 9,respectively, about their outer peripheral surfaces upon which thetappet follower (not shown) of the respective intake and exhaust valvesride for controlling the flow of gases between intake and exhaust portscommunicating with the engine combustion chamber. As shown, theprojecting portions of cam lobes 3, 4 are offset with respect to oneanother about 90° so as to cyclically open its respective valve duringengine operation, as is conventional.

Referring now to FIG. 3, there is illustrated in detail cam profile 8.As shown, cam profile 8 is "stepped" and includes a shoulder 10 formedin the peripheral surface of cam profile 8 between opposite axial ends11, 12 of cam lobe 3. Shoulder 10 is defined by a first axiallyextending tapered surface 13 and a second axially extending taperedsurface 14 which extends parallel to tapered surface 13. As shown,tapered surface 13 extends axially from end 11 of cam lobe 3 to theupper edge of shoulder 10 such that the upper edge of shoulder 10extends a radial distance outwardly of end 11. Tapered surface 14extends axially from shoulder 10 to the opposite end 12 of cam lobe 3.Tapered surface 14 extends from the lower edge or radially inner edge ofshoulder 10 to the edge of end 12 such that the edge of end 12 islocated at a radial distance equal to or less than the radial extent ofthe upper edge of shoulder 10, as shown best by the horizontal line 15in FIG. 3. As shown best in FIG. 1, shoulder 10 extends around theentire profile 8 of cam lobe 3.

Referring to FIG. 4, there is illustrated an alternate form of camprofile 8. The stepped profile 8 of FIG. 4 is similar to thatillustrated in FIG. 3 and therefore like numerals except with thesubscript "a" are utilized for like elements. However, step or shoulder10 of profile 8 in FIG. 3 is replaced by a transition shoulder or step32 including external radius 33 and internal radius 34.

Referring now to FIG. 5, there is illustrated a fragmentary view showinga portion of the mold for making camshaft assembly 1. More specifically,FIG. 5 illustrates a cam lobe 18 integrally molded together with ahollow sleeve 19 in a manner similar to that shown in FIG. 1, exceptthat profile 20 of cam lobe 18 is "arcuate" in shape instead of being"stepped" in shape. As illustrated, the apex of profile 20 has a radialdimension equal to or greater than the radial dimension of either ofopposite axial ends 21, 22 of cam lobe 18. This arcuate shape of theperipheral surface of cam profile 20 extends around the entire profile20 of cam lobe 18.

It should be noted that both the stepped cam profile 8 (see FIGS. 3 and4) as well as the arcuate profile 20 (see FIG. 5) may be defined asillustrating "crowned" cam lobes. Thus, the term "crowned cam profile"includes both the stepped profiles of FIGS. 3 and 4 as well as thearcuate profile of FIG. 5 so long as the high point of the profile has aradial dimension equal to or greater than the radial dimension of eitherof the opposite ends of the cam lobe.

Referring once again to FIG. 5, the mold shown therein includes anaxially movable die component 23, and a radially movable die component24 which form a mold cavity having a first portion 25 in the shape ofsleeve 19 and a second portion 26 in the shape of cam lobe 18 which, asillustrated, includes a "crowned" cam profile, i.e. in this case arcuateshaped. Thus, the second portion 26 of the mold cavity has an arcuateshaped surface 27 corresponding to profile 20 of cam lobe 18.

As illustrated, die component 23 is movable axially in the directionillustrated by arrow 28, and die component 24 is movable radially asillustrated by the arrow 29. However, under normal moldingcircumstances, die component 23 may not be moved axially since portion30 thereof would not clear the apex of cam profile 20 after molding, asis clearly evident from the fact that portion 30 extends radiallyinwardly of the apex of profile 20. Therefore, in order to permit diecomponent 23 to be pulled off axially, the present invention includes amethod of molding camshaft assembly 1 such that the mold cavity isfilled with a shrinkable fluid plastics material, and thereafter waitinga predetermined period of time to permit the plastics material in camlobe portion 26 of the mold cavity to simultaneously solidify and shrinkso that the apex of profile 20 of cam lobe 18 after shrinking isradially inwardly of the lower edge of portion 30 of die component 23,as indicated by the dotted line 31 in FIG. 5. In order to accomplishthis, the fluid plastics material must have a shrinkage rate of at leastabout 0.000067 inches per second. If the material does not have such ashrinkage rate, the cycle time for manufacturing such camshaftassemblies becomes excessively long and as a result more expensive. Suchmaterials are typically heated molten plastics material injected intothe mold cavity. Typical of such plastics material is a nylon basedmaterial such as reinforced or unreinforced nylon or a blend of nylonwith other plastics materials so long as the blend has the aboveshrinkage rate characteristic. The waiting time enables the moltenmaterial to cool for a period of time between 0 and 30 seconds,preferably less than 5 seconds, so that the material shrinkssufficiently to enable die component 23 to be moved axially to open themold cavity. As is apparent, the mold cavity must be initially overdimensioned so that upon shrinkage the proper radial dimension of camlobe 18 is obtained.

In order to demonstrate the advantages of making the camshaft assemblyor the cam gear assembly entirely of non-metallic or plastics materialto form either a composite or an all-plastic camshaft assembly, numeroussound tests were performed and various noise data was collected. Table Iillustrates a competitive engine evaluation which includes various smallengines typically utilized for lawn and garden type applications.

                  TABLE 1                                                         ______________________________________                                        Competitive Engine Noise Evaluation                                           4 Meter Energy Average (dB)                                                   Engine Make, Model                                                                           3200 RPM  3000 RPM  2700 RPM                                   ______________________________________                                        Engine #1, 1   73.8      72.5      70.9                                       Briggs & Stratton Max-40                                                                     73.5      72.5      71.0                                       Engine #2, 1   72.1      71.6      71.2                                       Engine #3, 1 OHV                                                                             72.1      71.1      69.9                                       Engine #3, 2 2-Stroke                                                                        71.6      70.9      69.7                                       Briggs & Stratton Quantum                                                                    70.7      69.7      67.5                                       Engine #4, 1 OHV                                                                             69.5      68.5      67.5                                       Engine #4, 2 OHV                                                                             70.4      --        68.7                                       Mower w/o Blade                                                               Engine #4, 3 OHV                                                                             --        --        67.0                                       Mower w/o Blade                                                               ______________________________________                                    

In the above Table I, the Briggs & Stratton Quantum engine hasincorporated therein a composite camshaft assembly comprising a metalliccamshaft, and an integrally molded cam gear, cam lobes and thrustbearings composed of a nylon material. Table I demonstrates that theBriggs & Stratton Quantum engine is significantly quieter with anaverage decibel reading of 69.3 at 4 meters over an operating range of2700 to 3200 revolutions per minute.

Table II demonstrates noise data obtained from two different model 929Briggs & Stratton engines utilizing a composite camshaft assemblysimilar to that utilized to obtain the data in Table I. The model 929engine included a muffler, intake silencer, and its drive shaft wasloaded with only an inertia disk. The noise data was taken at a 4 meterdistance over a range of 2700, 3000 and 3300 revolutions per minute.

                  TABLE II                                                        ______________________________________                                        Composite Camshaft Noise Tests                                                Briggs & Stratton Model 929 Engine                                            Muffler, Intake Silencer, Inertia Disk Load                                                4M. Energy Average (dB)                                                       3300 RPM                                                                              3000 RPM  2700 RPM                                       ______________________________________                                        1.  Engine #1, with                                                                              73.1      71.6    70.2                                         Std. Metal Assembly                                                       2.  Engine #1, with                                                                              70.5      68.6    66.7                                         Composite Assembly                                                        3.  Engine #2, with                                                                              72.5      71.4    70.6                                         Std. Metal Assembly                                                       4.  Engine #2, with                                                                              69.6      68.2    67                                           Composite Assembly                                                        ______________________________________                                    

As can be seen from the above data in Table II, the camshaft assembly ofthe present invention significantly reduces the noise emanating from anengine.

The following Table III was another test performed to obtain noise dataon a model 94908 Briggs & Stratton engine including an air vane governorthereon. The tests were performed with different types of camshaftassemblies with the pinion on the crankshaft which drove the cam gearhaving various mounting arrangements. The noise data was obtained at 4meters over a range of 2400 to 3200 revolutions per minute.

                                      TABLE III                                   __________________________________________________________________________    Camshaft Noise Tests                                                          Briggs & Stratton Model 94908 w/Air Vane Governor                             4M. Energy Average (dB)                                                       Test              3200 RPM                                                                            3000 RPM                                                                            2700 RPM                                                                            2400 RPM                                  __________________________________________________________________________      Standard metal assembly keyed                                                                 70.3  69.9  68.1  67.0                                        pinion on crankshaft                                                          Composite assembly keyed pinion                                                               70.1  68.9  66.9  65.6                                        on crankshaft/2 intake springs                                                Composite assembly/integral                                                                   70.1  68.8  67.3  65.1                                        pinion on crankshaft/2 intake                                                 springs                                                                       Standard metal assembly/integral                                                              72.9  72.1  71.1  69.8                                        pinion on crankshaft/standard                                                 exhaust spring                                                              __________________________________________________________________________

The above data from Table III once again illustrates that a camshaftassembly in accordance with the present invention substantially reducesthe noise as compared to standard as well as other types of camshaftassemblies.

Referring now to Table IV, there is shown a further noise comparisonbetween the camshaft assembly of the present invention incorporated in amodel 8 Briggs & Stratton quiet engine and a standard model 8 Briggs &Stratton quiet engine. The standard model 8 engine utilized aconventional metallic camshaft assembly. Both engines were fitted withan infinite muffler and an intake silencer. The noise data was taken ata 1 meter distance and the tests were run under full load and no loaddrive shaft conditions at both 3000 and 3600 rpms.

                  TABLE IV                                                        ______________________________________                                        Noise Comparison                                                              Composite Camshaft vs. Standard Camshaft                                      Briggs & Stratton Model 8 Quiet Engines                                       Infinite Muffler - Intake Silencer                                            1M. Energy Average (dB)                                                                       3600 RPM 3000 RPM                                                               Full    No     Full  No                                     Test              Load    Load   Load  Load                                   ______________________________________                                        1.   Standard Quiet Model 8                                                                         82.6    79.4 81.4  77.4                                      (Average of 4)                                                           2.   Composite Camshaft                                                                             80.1    75   77.4  72.8                                      TR #10062                                                                ______________________________________                                    

Once again, the data shown in Table IV illustrates a substantialreduction in noise when the composite camshaft of the present inventionis incorporated in a standard model 8 Briggs & Stratton engine.

Finally, additional noise tests were run on a model 60102 Briggs &Stratton engine in order to test six different composite camshaftassemblies made from production tooling. Table V summarizes the noisedata obtained therefrom. The model 60102 engine included an infinitemuffler and intake silencer and the readings were taken at 1 meter withno load on the engine drive shaft. In this test, the primary concern waswith no load mechanical noise, and therefore the tests were run with aninfinite muffler and intake silencer. All the no load test results aresummarized in Table V.

                                      TABLE V                                     __________________________________________________________________________    Composite Camshaft Noise Tests Briggs & Stratton Model 60102                  Engine Infinite Muffler - Intake Silencer 1 Meter Energy Average (dB) No      Load                                                                          Test              3600 RPM                                                                            3300 RPM                                                                            3000 RPM                                                                            2700 RPM                                                                            2400 RPM                            __________________________________________________________________________      Standard Metal Assembly                                                                       79    78    77.5  76.4  75.5                                  2-C1 Composite Nylon Assembly                                                                 77.3  75.5  73.2  72    70.6                                  2-C2 Composite Nylon Assembly                                                                 75.6  74.4  72.8  71.3  69.5                                  1-C1 Composite Nylon Assembly                                                                 76.3  74.1  72 7  71.2  70.4                                  1-C3 Composite Nylon Assembly                                                                 76.1  74.1  73.1  71.2  69.6                                  2-C3 Composite Nylon Assembly                                                                 75.4  73.5  72.5  70.6  69.7                                  1-C4 Composite Nylon Assembly                                                                 75.7  73.6  72.7  71    69.4                                  2-C1 Repeat     77    74.7  72.8  71.3  69.3                                  Average (Tests 2-7)                                                                           76.1  74.2  72.8  71.2  69.9                                10.                                                                             Average reduction from                                                                         2.9   3.8   4.7   5.2   5.6                                  standard metal assembly                                                     __________________________________________________________________________

As shown from the above data, there was almost a 3 decibel average noisereduction at 3600 rpms. The improvements increase with lowered enginespeed until an average of about 5.6 decibels of noise reduction wasobtained at 2400 rpm. One camshaft assembly, namely 2-Cl, did notperform as well as the others. The 2-Cl camshaft assembly was 1.5decibel higher than the average of the other 5 camshaft assemblies at3600 rpm. A later or second retest confirmed the higher noise levels.The character of the noise appeared to indicate some type of valveimpact noise, and a careful check of the cams revealed a fairly largedeviation of the exhaust cam profile for 2-Cl. This deviation wouldchange the valve velocity and acceleration and could cause excessivenoise from valve seat impact or lifter impact. However, even with all ofthe faults of the 2-Cl, the 2-Cl still tested 1.7 decibels quieter at3600 rpm than the standard metal assembly.

The present invention thus provides a camshaft assembly for engine usewhich has numerous advantages with quiet operation and low manufacturingcosts being two of the most desirable advantages.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

We claim:
 1. A method of molding an internal combustion engine camshaftassembly including a camshaft and an integral cam lobe and with saidlobe having a crowned cam profile with an apex, comprising the stepsof:(a) providing a mold including a die component axially closeable todefine a mold cavity having first surface portions in the shape of acamshaft which defines an axis of rotation and having second surfaceportions shaped to define the cam lobe of the assembly, said secondsurface portions including a radially outer surface delineating thecrowned cam profile and apex of the cam lobe, said apex of said radiallyouter surface being disposed radially outwardly of a lower edge of aportion of said die component, (b) filling said mold cavity with ashrinkable fluid plastics material so that said material forms acamshaft assembly conforming to the shape of and initially engaging saidfirst and second surface portions of said mold cavity, (c) delaying fora predetermined period of time so that said plastics material hardensand shrinks radially inwardly away from said radially outer mold cavitysurface until the apex portion of the camshaft assembly cam profile isfinally disposed radially inwardly of said lower edge of said diecomponent portion, (d) and then opening said mold by moving said diecomponent only in an axial direction so that said lower edge of said diecomponent portion passes freely over said apex portion of the camshaftassembly cam profile.
 2. The method of claim 1 wherein said plasticsmaterial is a nylon based material.
 3. The method of claim 1 wherein thefilling step comprises injecting molten plastics material into the moldcavity.
 4. The method of claim 1 wherein the fluid plastics materialcomprises a heated molten plastics material and the step of delayingcomprises cooling the molten material for a period of time between 0 and30 seconds.
 5. The method of claim 1 wherein the fluid plastics materialcomprises a heated molten plastics material and the step of delayingcomprises cooling the molten material for a period of time less than 5seconds.
 6. The method of claim 1 wherein said plastics material has ashrinkage rate of at least about 0.000067 inches/second.